Tea is a beverage made from processed tea leaves and hot or boiling water. The four major types of tea (black, oolong, green and white) are considered functional foods because they naturally contain chemicals associated with certain health benefits. Each type of tea contains tannins, including catechins, which act as antioxidants in the body, helping to prevent cellular damage. Tea also naturally contains caffeine, which acts as a stimulant in the body.

Each type of tea is made from the same plant, but differs in how they are processed. Processing differences result in varying tastes and level of antioxidants among the types. Black tea contains the least amount of antioxidants and white tea the most. In addition, tea that is brewed (rather than instant) and steeped for longer periods of time in hot water may contain more antioxidants.  

Moderate amounts of tea are considered safe for most people. However, it is not known how much tea should be consumed in order to gain its associated health benefits. Components in tea may interact with certain medications, medical conditions or stages of life, other foods or supplements. The caffeine in tea may cause gastrointestinal problems and insomnia. Caffeine is also habit-forming and may cause withdrawal symptoms if use is suddenly discontinued.

Herbal teas are made from herbs or plants other than the tea plant. Thus, they contain no tea and are sometimes referred to as herbal infusion or tisane. The safety and effectiveness of most herbs has not been scientifically proven. Problems may arise when herbal teas are consumed excessively, consumed to treat medical conditions or when unsafe herbs are consumed.

Tea extracts may be available in supplement form. However, there is a lack of well-designed scientific studies concerning the safety and effectiveness of tea supplements. In addition, adverse side effects have occurred with tea supplements. Most nutrition experts recommend getting nutrients and other healthy substances from foods rather than relying on supplements.

The U.S. Food and Drug Administration (FDA) has not approved any health claims associating tea use with any disease or medical condition. However, other types of claims (e.g., structure-function claims, nutrient content claims) may be allowed.

Marketers of herbal teas may avoid making health claims by including language such as “relaxing” or “soothing” on their labels. Consumers are advised to carefully read product labels before purchasing teas or herbal products, and to consult their physician or registered dietitian if they have doubts about whether a product is appropriate for use.